1. Field of the Invention
This application relates generally to the design of a full duplex speakerphone to be used in telecommunication systems (TSs) including stationary applications (e.g., conference speaker phones) and mobile applications (e.g., cellular phones, handset phones and handheld PDAs).
2. Background Art
Telecommunication systems are capable of operating in a speaker mode in which data is broadcast through the speakers, or in a handset mode in which data is output through an ear piece in the telecommunication system. Audio quality in telecommunication systems, especially in the speaker mode, is a feature that receives high consideration. A known issue affecting audio quality in the speaker mode is the non-linear distortion and echo propagating between the broadcasting speakers and microphones which are co-located on the telecommunication systems. As such, suppression of this non-linear distortion and echo is desired.
Generally, linear filters are used to cancel linear echo. However, linear filters cannot model non-linear distortion, and therefore are not effective in eliminating non-linear distortion. As a result, non-linear processing is used, which reduces voice conversation quality.
Further, complex second and third-order non-linear filters (e.g., Volterra filters) are known to better identify the non-linearities and achieve improved suppression of the same. However, implementation of the non-linear filters is computationally complex and expensive due to the large number of coefficients required to represent the non-linear filters. In addition, the equations required to update these non-linear filters are convoluted, requiring an enormous amount of processing. As such, the use of non-linear filters for suppression of non-linear distortion and echo is complex, expensive, and impractical.
Designing a full duplex speakerphone can also be difficult due to the complicated tuning of telecommunication systems, which can require customized audio tuning on a product-by-product basis. Finally, full duplex speakerphones are difficult to provide for telecommunication systems using conventional DSP techniques, especially for mobile applications where size and cost are the limiting factors. Thus, these limitations are primarily due to poor acoustic designs, inefficient components, and because these conventional techniques cannot account for non-linear distortion in the echo path.
What is needed is an improved configuration for a full duplex speaker phone.
The present invention will be described with reference to the accompanying drawings. The drawing in which an element first appears is typically indicated by the leftmost digit(s) in the corresponding reference number.